1. Field of the Invention
The present invention relates to an apparatus for inspecting the print quality of a series of barcodes positioned on a high speed moving web.
2. Description of the Prior Art
It is well known in the art of printing that the quality of the print on a moving web declines with prolonged use of the printing machine. Therefore, it is necessary to monitor the quality of the print to maintain high quality output. Present methods of inspection are done subjectively by human workers at scheduled intervals. This method requires visual inspection of print quality and thus is inaccurate and very expensive. This is inaccurate because it is very difficult for the human eye to recognize subtle differences in contrast value, especially when the web is moving at high speeds. Further, the inspections must be done in scheduled intervals, therefore a problem is not recognized when it first occurs, but rather when it is first noticed. Nor is this method is cost efficient, because it requires the use of an inspector to exercise subjective judgment to monitor the print quality on the web.
Various apparatus are known in the art to print and scan images on a given material. One such apparatus, as taught in U.S. Pat. No. 5,321,436, discloses a franking machine which implements barcode printing and reading on individual mail items. This apparatus scans barcodes, yet there is no pre-sensing and trigger of a scanner which senses the quality of the barcode. Further, this apparatus is utilized for scanning barcodes on individual mail items, rather than barcodes on a continuous moving web. One known method of inspecting the surface of a continuously moving web is found in U.S. Pat. No. 4,868,403. This method involves scanning the web with a scanning beam to detect surface defects. This system, however, has no barcode reading feature. Another known method of inspecting the surface of a continuously moving web is found in U.S. Pat. No. 4,683,380. This involves an apparatus for detecting perforations, rather than barcodes, on a web material.
A much more reliable and cost effective method of inspection is provided by this invention which uses an apparatus which scans for the presence of a barcode, deciphers the barcode data when recognized, and objectively monitors acceptable print quality of the barcodes on a continuously moving high speed web. The apparatus includes a synchronization element comprising a light source which emits incident light on a barcode position, and a photocell which monitors reflected light from the barcode or barcode marker. The synchronization element triggers the laser scanning element to read the barcode and decode scanned barcode data and checks it for validity. A microprocessor receives the barcode position data and instructs the laser scanning element to receive and decode scanned data and present the decoded data. In addition, a contrast sensor is employed which determines the print contrast of either black or color print as compared to the web background. The contrast of the print can be compared either to the background of the web material, to print on the opposite face of the printed web material, or to print on another location on the web material. If an erroneous print quality value or contrast value at a threshold amount is indicated, the apparatus stops the web until the problem is corrected.